Loquat Tree Disease or Pest Concern

Asked January 15, 2020, 3:23 AM EST

Hello OSU! I have a loquat (Japanese plum) tree in my back yard. It’s about 20-25 years old and is gorgeous! It has fruited many of the years I have lived in my home (10 years). I’m in North Portland. Late last summer, I found the bark peeling away in large areas. I believe a grub or something is eating the tree. I did find a small worm under one of the peeling chunks of bark but wasn’t sure if that’s the cause or just living/laying eggs there. Pics attached. The last pic has the worm, if you zoom in it’s pretty clear. It looks really bad, but I haven’t seen any of the tree tops dying back just yet. I’m very concerned and hope you can possibly help diagnose the problem so I know how to tackle it. The tree was planted by one of the owners of Xera Plants in Portland (when he lived here before me). I contacted him and sent pics asking for advice. He said he wasn’t sure but his research showed the tree is prone to a caterpillar pest, but those sources only referenced China & Alabama, nothing West Coast. He suggested reaching out to you all! Ideas? Help please! Thank you so much!

Multnomah County Oregon

3 Responses

Excessive nitrogen application increases the susceptibility of loquat trees to fire blight. Many other minor diseases have been reported to attack loquat including Pythophthora (crown rot), Psuedomonas eriobtoryae (cankers), scab, Diplodia natalensis (collar and root rot), and anthracnose. Fire blight is a very serious bacterial disease that first manifests in trees as a watery substance that drips from cankers on the branches, twigs or trunk. The substance eventually darkens, leaving stains on the branches or trunk. Fire blight can shrivel and blacken fruit, and seriously damage the overall health of the tree. In spring, branch and trunk canker symptoms can appear as soon as trees begin active growth. The first sign is watery, light tan bacterial ooze that exudes from cankers (small to large areas of dead bark that the pathogen killed during previous seasons) on branches, twigs, or trunks. The ooze turns dark after exposure to air, leaving streaks on branches or trunks. However, most cankers are small and inconspicuous; thus infections might not be noticed until later in spring when flowers, shoots, and/or young fruit shrivel and blacken. The amount of fruit loss depends upon the extent and severity of the disease.To help combat fire blight, prune away infected branches with sterile equipment, and burn all infected material. Chemical controls are available to help prevent future outbreaks.

Here are some publications that may be useful.

https://aggie-horticulture.tamu.edu/citrus/loquat.htm

http://ipm.ucanr.edu/PMG/PESTNOTES/pn7414.html

Hope this helps!

Thank you for your reply & the resources shared. The flowers/fruit/leaves don’t turn black and remain on the tree, a few other symptoms don’t really match up either. Did your research happen to turn up any other likely causes? I’ll need to find an arborist, but if you have any second guesses I’d welcome them. Thanks so much, I appreciate your time.

This could be caused by a borer insect, like peach tree borer that can attack plums and cherries also. Peach borer larvae tunnel through cracks and wounds within bark, feeding on the sapwood. Peach tree borers attack near the soil line, with most activity occurring a few inches below the ground. Eventually, the bark begins to peel off damaged areas, making the tree susceptible to other pests and disease.

Adults, which resemble wasps, are most prevalent from mid-May to early October. During this time, eggs are laid on the trunks of trees, hatching within a week.

Peach tree borer control can be difficult, as the larvae are not easily accessible beneath the tree bark. Most effective control methods consist of preventive insecticides targeted at the egg or early larval stage. These usually contain permethrin.

I also considered a bacterial canker called pseudomonas. This causes stem cankers: depressed areas in the bark, which darken with age. A gummy substance often exudes from cankers on fruiting and flowering stone fruits (this symptom is referred to as “gummosis”). If cankers continue to enlarge, they may girdle the stem and subsequently kill a branch or the entire plant. If the outer tissues of the canker area are cut away, the tissue underneath shows a reddish-brown discoloration. This discoloration may also occur as vertical streaks in the vascular tissue. Wounding of any kind seems to play a major role in initiating disease development. Wounds may be mechanical or environmental such as frost injury. Wounds have been shown to predispose trees to blossom blight and bacterial canker. Pruning wounds not only allow the bacterium to enter but also aid infection by fungi such as Cytospora and Nectria.

Here is some information about this problem.

https://pnwhandbooks.org/plantdisease/pathogen-articles/pathogens-common-many-plants/bacteria-other-prokaryotes/diseases

Hope this helps further!